This invention generally relates to a system and method for providing regulated flow of oxygen, including for flight crew or passengers on-board an aircraft. The invention more particularly relates to a system and method for ensuring that oxygen gas suitable for breathing is promptly and intermittently available to flight crew or passengers on-board an aircraft including during an aircraft's descent. Components of the system include oxygen generators and a heat exchanger interface for transferring heat from the exothermic decomposition reactions of a first oxygen generator to a second heat-dependent oxygen generator.
Conventional systems and methods for supplying oxygen to aircraft passengers typically rely upon gaseous oxygen that is either chemically generated in a passenger service unit (PSU) located above a passenger seat, or dispensed from pressurized gaseous cylinders, typically either through a centralized distribution network on the aircraft or from a plurality of separate individualized gaseous cylinders.
When the emergency oxygen is to be supplied to a face mask, a constant flow of oxygen is typically received by a reservoir bag attached to the face mask. The oxygen is commonly supplied continuously at a rate that is calculated to accommodate even the needs of a passenger with a significantly larger than average tidal volume who is breathing at a faster than average respiration rate. The continuing flow of oxygen into the reservoir bag and into the mask is typically diluted by cabin air.
Chemically generated oxygen systems are provided as single use devices that once activated can only be used once and must be replaced for future use. Chemically generated oxygen systems are generally suitable for shorter duration flights, under 22 minutes. However, the terrain of the flight path is also a determining factor in the suitability of chemically generated oxygen systems to meet oxygen demands. For longer duration flights and flights subject to variable or challenging terrain, gaseous oxygen can be stored in cylinders. Oxygen from pressurized cylinders of gas may be distributed from one or more sources within a distribution network of an aircraft, or individual cylinders may be provided for each passenger or crew member. In either case, given the limited space of an aircraft, oxygen from the cylinders is typically not far from components of the aircraft's illumination system increasing the hazard potential. For example, individual cylinders or outlets of a distribution network above the seats are near the lights. The extensive plumbing required throughout the aircraft to incorporate these pressurized oxygen cylinders as part of the on-board oxygen supply system for oxygen distribution to passengers must be periodically leak checked, which increases maintenance costs. Pressurized oxygen cylinders also have to be sufficiently strong so as to prevent burst hazards, which leads to increased weight, and consequently increased fuel consumption and fuel cost.
Enhancing the efficiency of such aircraft emergency oxygen supply systems either in terms of the generation, storage, distribution or consumption of oxygen could therefore yield a weight savings. Conversely, an enhancement of an aircraft emergency oxygen supply system's efficiency without a commensurate downsizing would impart a larger margin of safety in the system's operation. It is therefore highly desirable to enhance the efficiency of an emergency or supplemental oxygen supply system in any way possible.
The delivered supplemental oxygen flow rate needed to properly oxygenate an aircraft cabin occupant depends on the prevailing atmospheric pressure at a given altitude. The quantity and rate of flow of oxygen delivered to a user can advantageously be varied as a function of altitude, to provide proper oxygenation, while avoiding an inefficient and wasteful delivery of a greater quantity of oxygen than is required.
A molecular sieve oxygen generating system (MSOG) is also known that generates a supply of oxygen or an oxygen enriched gas and a residual gas from a supply gas. Such molecular sieve oxygen generator type of on-board oxygen generator devices rely on pressure swing adsorption (PSA) technology to produce an oxygen enriched gas comprising up to 95% oxygen with a residual gas stream that can contain greater than about 9% oxygen. However, this system has limited applicability for meeting aircraft passenger demands for oxygen in the initial stages of operation, which may be required immediately at high altitudes. Further, this system does not minimize consumption of oxygen or conserve oxygen.
Pressure swing adsorption technology, incorporated in molecular sieve oxygen generating systems, is based on the principle that gases under pressure are generally attracted to solid surfaces upon which the gases are adsorbed. Higher pressure results in greater gas adsorption. When the pressure is reduced or swings from high to low, gas is released or desorbed. Gaseous mixtures may be separated through pressure swing adsorption because different gases tend to be adsorbed or attracted to different solid materials to varying degrees.
Accordingly, when the pressure is reduced gases that are less strongly attracted to the solid materials will be desorbed first to form an outlet stream. After the bed of solid material to which gases are adsorbed reaches its capacity to adsorb, pressure is further reduced to release more strongly attracted gases. As applied to an on-board oxygen generator (OBOG), engine bleed air is typically fed into the pressure swing adsorption device, the nitrogen component of air is adsorbed to a bed of solid material more strongly than the oxygen component of air, and a gaseous outlet stream enriched with oxygen is produced.
Adsorbents for pressure swing adsorption systems must have the ability to discriminate between two or more gases demonstrating selective adsorption. Suitable adsorbent materials for pressure swing adsorption systems are usually very porous materials selected for their large surface areas, for example activated carbon, silica gel, alumina and zeolites. The gas adsorbed on these surfaces may consist of a layer that is only one or at most a few molecules thick. Adsorbent materials having surface areas of several hundred square meters per gram enable the adsorption of a significant portion of the adsorbent's weight in gas. The molecular sieve characteristics of zeolites and some types of activated carbon called carbon molecular sieves serve to exclude some gas molecules based on size, in addition to the differential adsorption selectivity for different gases.
Another system is known that utilizes molecular sieve bed and/or permeable membrane technology, to produce first, oxygen for use for breathing by an aircrew, and second, nitrogen for use as an inert environment in the fuel tanks of an aircraft. However such systems still require the provision of compressors for both the oxygen, in order that the oxygen can be delivered at an appropriate pressure for breathing, and for the nitrogen. Also, the concentration of oxygen which can be produced is restricted by virtue of the nature of the conventional on-board oxygen generator device technology which is used. Due to the high temperature requirement there is a time lag before full oxygen capacity can be utilized.
Another type of on-board oxygen generator is a ceramic oxygen generator (COG), which utilizes solid electrolyte oxygen separation (SEOS) technology in which oxygen is catalytically separated from air inside specialized ceramic materials at high temperatures, about 650° C. to 750° C., typically using electrical voltage to supply the heat required. While this process can produce substantially pure oxygen gas product at pressure suitable for breathing at any altitude, including higher altitudes over 30,000 feet, the oxygen is not promptly available upon powering on of the device because the device has to reach the required operating temperature first.
While ceramic oxygen generator devices typically are superior to molecular sieve oxygen generator devices based on an ability to provide purer or more highly concentrated oxygen-enriched gas at pressures suitable for breathing, oxygen from ceramic oxygen generator devices is also not promptly available due to the high temperature requirement necessary for oxygen generation from such devices.
When an emergency situation arises on-board an aircraft, oxygen that is promptly available at a concentration, temperature, and pressure suitable for breathing is needed. At high altitudes, greater than 30,000 feet, 99% purity or higher oxygen gas is required. At lower altitudes, equal to or less than 30,000 feet, oxygen gas that is 90-95% oxygen may be suitable. An emergency situation may include sudden cabin decompression, sudden descent, and the like.
It would be desirable to provide a system that utilizes the advantages of ceramic oxygen generator devices incorporating solid electrolyte oxygen separation technology without sacrificing availability of breathable oxygen gas in the short-term during descent or upon an emergency situation arising by integrating ceramic oxygen generator devices with other sources that provide oxygen in the short-term. Ideally, such a system would also conserve oxygen and maximize efficiency of oxygen usage.
It would further be desirable to conserve oxygen that is available or generated by providing oxygen to the masks of passengers or crew intermittently, utilizing a feedback mechanism such that oxygen is provided as needed with a margin allowed for safety.
Finally, it would be highly desirable to reduce the wait time required for the supply of oxygen from ceramic oxygen generator systems incorporating solid electrolyte oxygen separation technology by heating the ceramic membranes upon which these systems rely more rapidly. The present invention meets these and other needs.